Active shielding device and method of active shielding

ABSTRACT

Embodiments of an active shielding device and method for active shielding are disclosed. In an embodiment, an active shielding device includes current sources configured to generate currents, an analog wire shield unit connected to the current sources, switches connected between the current sources and the analog wire shield unit, a current to voltage converter connected to the analog wire shield unit and configured to generate a voltage in response to the currents that are generated by the current sources and a digital control sequence for the switches, a voltage comparator connected to the current to voltage converter and configured to compare the voltage that is generated by the current to voltage converters with a reference voltage, a digital active shielding unit connected to the current sources, digital logics configured to process the digital control sequence before conducting the digital control sequence through the digital active shielding unit and after conducting the digital control sequence through the digital active shielding unit to generate a first processing result signal and a second result signal, and a digital comparator configured to compare the first processing result signal with the second result signal.

BACKGROUND

Invasive attacks can be used to illicitly access information from acircuit, such as a cryptographic circuit or a security circuit, or alterinformation at a circuit. Probing is one type of invasive attacks thatcan be used by an attacker to read data from an Integrated Circuit (IC)chip or to write data into an IC chip through a port (i.e., the probetip). For example, a focused ion beam (FIB) device can cut one or moretracks in a metal layer of an IC chip and subsequently altering thestructure of the IC chip, e.g., by depositing one or more new tracks orisolation layers into the IC chip and/or by implanting ions to changethe doping of an area of semiconductor substrate (e.g., silicon) of theIC chip. To protect against invasive attacks, active shieldingtechnology can be used to detect if a circuit is tampered with. Forexample, digital active shielding can form a physical barrier of signallines across an IC chip and shut down the IC chip in case the IC chip istampered with. However, although digital active shielding can offerprotection against invasive attacks, digital signals that are at 0/1levels can be hacked through long-term monitoring. Therefore, there is aneed for active shielding technology that can provide more complexprotection against invasive attacks.

SUMMARY

Embodiments of an active shielding device and method for activeshielding are disclosed. In an embodiment, an active shielding deviceincludes current sources configured to generate currents, an analog wireshield unit connected to the current sources, switches connected betweenthe current sources and the analog wire shield unit, a current tovoltage converter connected to the analog wire shield unit andconfigured to generate a voltage in response to the currents that aregenerated by the current sources and a digital control sequence for theswitches, a voltage comparator connected to the current to voltageconverter and configured to compare the voltage that is generated by thecurrent to voltage converters with a reference voltage, a digital activeshielding unit connected to the current sources, digital logicsconfigured to process the digital control sequence before conducting thedigital control sequence through the digital active shielding unit andafter conducting the digital control sequence through the digital activeshielding unit to generate a first processing result signal and a secondresult signal, and a digital comparator configured to compare the firstprocessing result signal with the second result signal.

In an embodiment, the digital active shielding unit includes an evennumber of inverters.

In an embodiment, the digital logics are identical to each other.

In an embodiment, one of the digital logics is connected to the switchesthrough the digital active shielding unit.

In an embodiment, the current sources are connected in parallel to eachother.

In an embodiment, the analog wire shield unit includes analog wirewindings that are connected between the current sources and the currentto voltage converter.

In an embodiment, each of the analog wire windings is connected to adifferent current source of the current source.

In an embodiment, the active shielding device further includes acontroller configured to generate the digital control sequence.

In an embodiment, the controller includes a random number generator.

In an embodiment, an active shielding device includes first, second,third, and fourth sets of current sources, where each of the first,second, third, and fourth sets of current sources is configured togenerate currents, an analog wire shield unit connected to the secondand fourth sets of current sources, first, second, third, and fourthsets of switches that are connected to the first, second, third, andfourth sets of current sources, respectively, and are controlled by adigital control sequence, a first current to voltage converter connectedto the first set of current sources and to the fourth set of currentsources through the analog wire shield unit and configured to generate afirst voltage in response to the currents that are generated by thefirst and fourth sets of current sources, a first voltage comparatorconnected to the first current to voltage converter and configured tocompare the first voltage with a first reference voltage, a secondcurrent to voltage converter connected to the second set of currentsources and to the third set of current sources through the analog wireshield unit and configured to generate a second voltage in response tothe currents that are generated by the second and third sets of currentsources, a second voltage comparator connected to the second current tovoltage converter and configured to compare the second voltage with asecond reference voltage, a third voltage comparator configured tocompare results from the first voltage comparator and from the secondvoltage comparator, a digital active shielding unit connected to thesecond and third sets of current sources, digital logics configured toprocess the digital control sequence before conducting the digitalcontrol sequence through the digital active shielding unit and afterconducting the digital control sequence through the digital activeshielding unit to generate a first processing result signal and a secondresult signal, and a digital comparator configured to compare the firstprocessing result signal with the second result signal.

In an embodiment, the digital active shielding unit includes an evennumber of inverters.

In an embodiment, the digital logics are identical to each other.

In an embodiment, one of the digital logics is connected to the switchesthrough the digital active shielding unit.

In an embodiment, each current source within one of the first, second,third, and fourth sets of current sources is connected in parallel toeach other.

In an embodiment, the analog wire shield unit includes analog wirewindings that are connected between the fourth set of current sourcesand the first current to voltage converter and between the second set ofcurrent sources and the second current to voltage converter.

In an embodiment, the first set of switches are connected between thefirst set of current sources and the first current to voltage converter,the second set of switches are connected between the second set ofcurrent sources and the analog wire shield unit, the third set ofswitches are connected between the third set of current sources and thesecond current to voltage converter, and the fourth set of switches areconnected between the fourth set of current sources and the analog wireshield unit.

In an embodiment, the active shielding device further includes acontroller configured to generate the digital signal sequence to controlthe first, second, third, and fourth sets of switches.

In an embodiment, the controller includes a random number generator.

In an embodiment, a method for active shielding involves generatingcurrents using an active shielding device, conducting the currentsthrough analog wire windings of an active shielding unit of the activeshielding device in response to a digital control sequence, generating avoltage in response to the currents using a current to voltage converterof the active shielding device, comparing the voltage with a referencevoltage using a voltage comparator of the active shielding device,processing the digital control sequence before conducting the digitalcontrol sequence through inverters of an active shielding unit of theactive shielding device and after conducting the digital controlsequence through the inverters using digital logics of the activeshielding device to generate a first processing result signal and asecond result signal, respectively, and comparing the first processingresult signal with the second result signal.

In an embodiment, the digital active shielding unit includes an evennumber of inverters, and wherein the digital logics are identical toeach other.

Other aspects in accordance with the invention will become apparent fromthe following detailed description, taken in conjunction with theaccompanying drawings, illustrated by way of example of the principlesof the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts an active shielding device in accordance with anembodiment of the invention.

FIG. 2 depicts an embodiment of an analog wire shield unit of the activeshielding device depicted in FIG. 1.

FIG. 3 depicts an embodiment of a current to voltage converter of theactive shielding device depicted in FIG. 1.

FIG. 4 depicts an embodiment of a voltage comparator of the activeshielding device depicted in FIG. 1.

FIG. 5 depicts an active shielding device that includes multipleswitches to control multiple current sources in accordance with anembodiment of the invention.

FIG. 6 depicts an active shielding device that includes multiple sets ofcurrent sources, multiple current to voltage converters, and multiplevoltage comparators in accordance with an embodiment of the invention.

FIG. 7 depicts an active shielding device that includes multipleswitches to control current sources in accordance with an embodiment ofthe invention.

FIG. 8 depicts an active shielding device that includes a combination ofa digital shielding unit and an analog wire shield unit in accordancewith an embodiment of the invention.

FIG. 9 is a process flow diagram of a method of communications inaccordance to an embodiment of the invention.

FIG. 10 is a process flow diagram of a method of communications inaccordance to another embodiment of the invention.

Throughout the description, similar reference numbers may be used toidentify similar elements.

DETAILED DESCRIPTION

It will be readily understood that the components of the embodiments asgenerally described herein and illustrated in the appended figures couldbe arranged and designed in a wide variety of different configurations.Thus, the following more detailed description of various embodiments, asrepresented in the figures, is not intended to limit the scope of thepresent disclosure, but is merely representative of various embodiments.While the various aspects of the embodiments are presented in drawings,the drawings are not necessarily drawn to scale unless specificallyindicated.

The present invention may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. The describedembodiments are to be considered in all respects only as illustrativeand not restrictive. The scope of the invention is, therefore, indicatedby the appended claims rather than by this detailed description. Allchanges which come within the meaning and range of equivalency of theclaims are to be embraced within their scope.

Reference throughout this specification to features, advantages, orsimilar language does not imply that all of the features and advantagesthat may be realized with the present invention should be or are in anysingle embodiment of the invention. Rather, language referring to thefeatures and advantages is understood to mean that a specific feature,advantage, or characteristic described in connection with an embodimentis included in at least one embodiment of the present invention. Thus,discussions of the features and advantages, and similar language,throughout this specification may, but do not necessarily, refer to thesame embodiment.

Furthermore, the described features, advantages, and characteristics ofthe invention may be combined in any suitable manner in one or moreembodiments. One skilled in the relevant art will recognize, in light ofthe description herein, that the invention can be practiced without oneor more of the specific features or advantages of a particularembodiment. In other instances, additional features and advantages maybe recognized in certain embodiments that may not be present in allembodiments of the invention.

Reference throughout this specification to “one embodiment”, “anembodiment”, or similar language means that a particular feature,structure, or characteristic described in connection with the indicatedembodiment is included in at least one embodiment of the presentinvention. Thus, the phrases “in one embodiment”, “in an embodiment”,and similar language throughout this specification may, but do notnecessarily, all refer to the same embodiment.

FIG. 1 depicts an active shielding device 100 in accordance with anembodiment of the invention. In the embodiment depicted in FIG. 1, theactive shielding device includes multiple current sources 102-1, 102-2,. . . , 102-N, where N is an integer that is greater than one, an analogwire shield unit 104 connected to the current sources, a current tovoltage converter 106 connected to the analog wire shield unit, and avoltage comparator 108 connected to the current to voltage converter.The active shielding device is used to protect a circuit to be protected110, which can be a cryptographic circuit, a security circuit, or othercircuit, which can be connected to electrical wires or cables within theanalog wire shield unit, electrical wires or cables between the currentsources and the analog wire shield unit, or electrical wires or cablesbetween the analog wire shield unit and the current to voltageconverter. The active shielding device can be used in variousapplications, such as automotive applications, communicationsapplications, industrial applications, medical applications, computerapplications, and/or consumer or appliance applications. Although theillustrated active shielding device 100 is shown with certain componentsand described with certain functionality herein, other embodiments ofthe active shielding device may include fewer or more components toimplement the same, less, or more functionality. For example, the activeshielding device may include more than one analog wire shield unit. Inanother example, in some embodiments, the active shielding device mayinclude more than one current to voltage converter and more than onevoltage comparator. In yet another example, although the current sources102-1, 102-2, . . . , 102-N are shown in FIG. 1 as being part of theactive shielding device, in some embodiments, the current sources areexternal to the active shielding device and are not components of theactive shielding device. In some embodiments, the active shieldingdevice is an active shielding circuit. Components of the activeshielding circuit may be implemented on a single substrate (e.g.,integrated into the same IC chip) or distributed on multiple substrates(e.g., implemented on multiple IC chips). For example, at least one ofthe current sources, the analog wire shield unit, the current to voltageconverter, and the voltage comparator is implemented on a singlesubstrate (e.g., integrated into one IC chip) or distributed on multiplesubstrates (e.g., implemented on multiple IC chips). In someembodiments, the active shielding device and the circuit to be protectedare integrated into the same IC chip.

Compared to an active shielding device that relies solely on digitalshielding, the active shielding device 100 depicted in FIG. 1 implementsanalog active shielding that can be used independent from digital activeshielding or in combination with digital active shielding. In theembodiment depicted in FIG. 1, the active shielding device uses multiplecurrent sources 102-1, 102-2, . . . , 102-N and the analog wire shieldunit 104 for active shielding. Performance of active shielding incurrent domain is better than active shielding in voltage domain due toless noise injection. Current values from the analog current sources canbe generated randomly, in form of a known pattern, or a combination ofthem. In addition, digital probing or applying 0/1 to the analog wireshield unit can be detected easily. For example, any invasive attackthat cuts one or more electrical wires or cables within the analog wireshield unit 104 or applies 0/1 to one or more electrical wires or cableswithin the analog wire shield unit affects one or more currents that aregenerated by the current sources 102-1, 102-2, . . . , 102-N, andchanges the voltage range.

In the embodiment depicted in FIG. 1, the current sources 102-1, 102-2,. . . , 102-N are configured to generate multiple currents, I₁, I₂, . .. , I_(N). The current sources can be implemented using various types ofcurrent sources that are known in the art. In some embodiments, thecurrents generated by the current sources are different from each other(i.e., each current source generates a unique current). In otherembodiments, at least two of the currents, I₁, I₂, . . . , I_(N),generated by the current sources are identical to each other. In theembodiment depicted in FIG. 1, the current sources are connected inparallel to each other such that each of the currents, I₁, I₂, . . . ,I_(N), flows through the analog wire shield unit 104 in parallel. Insome embodiments, the current sources are connected to positivevoltages, which may be identical with each other or different from eachother.

In the embodiment depicted in FIG. 1, the analog wire shield unit 104 isconnected between the current sources 102-1, 102-2, . . . , 102-N andthe current to voltage converter 106. The analog wire shield unit mayinclude one or more electrical cables or wires, which are made ofconductive materials (e.g., metals). In some embodiments, the analogwire shield unit includes multiple analog wire windings that areconnected between the current sources and the current to voltageconverter. In these embodiments, each of the current sources isconnected to a different analog wire winding of the analog wirewindings.

FIG. 2 depicts an analog wire shield unit 204, which is an embodiment ofthe analog wire shield unit 104 depicted in FIG. 1. However, the analogwire shield unit 104 depicted in FIG. 1 is not limited to the embodimentshown in FIG. 2. In the embodiment depicted in FIG. 3, the analog wireshield unit 204 includes multiple analog wire windings 228-1, 228-2, . .. , 228-N that are connected to the current sources 102-1, 102-2, . . ., 102-N and to the current to voltage converter 106. In the analog wireshield unit, each of the analog wire windings is connected to adifferent current source. For example, currents, I₁, is conductedthrough the analog wire winding 228-1 to the current to voltageconverter, currents, I₂, is conducted through the analog wire winding228-2 to the current to voltage converter, and currents, I_(N), isconducted through the analog wire winding 228-N to the current tovoltage converter. In some embodiments, at least one of the analog wirewindings 228-1, 228-2, . . . , 228-N is implemented on a topmost layeror topmost layers of an IC chip into which the active shielding device100 is packaged. Security routing may be implemented on metal layers tominimal pitch and Arithmetic logic unit (Alu) width. In someembodiments, unused channels and/or spaces are filled to produce ashielded layout, which can thwart optical inspection and/or probing. Insome embodiments, randomized routing is used in parallel and multi-layerinterconnection is combined with a high metal density, which makes itmore difficult for an attacker to get access to the relevant informationin lower metal layers. In some embodiments, lower metals layers are usedfor signal lines and supply lines, which are not visible or accessiblevia pin connections. In some embodiments, lower metal layers are usedfor analog blocks with exception of ground and supply lines. Althoughthe illustrated analog wire shield unit is shown with certain componentsand described with certain functionality herein, other embodiments ofthe analog wire shield unit may include fewer or more components toimplement the same, less, or more functionality. For example, the analogwire shield unit may include more analog wire windings or less analogwire windings as shown in FIG. 2. In another example, although theanalog wire windings 228-1, 228-2, . . . , 228-N are shown in FIG. 2 ashaving wire windings in certain form or style, in other embodiments, atleast one of the analog wire windings 228-1, 228-2, . . . , 228-N mayhave a wire winding in a form or style that is different from the formor style shown in FIG. 2.

Turning back to FIG. 1, the current to voltage converter 106 of theactive shielding device 100 is configured to generate at least onevoltage in response to the currents, I₁, I₂, . . . , I_(N), that aregenerated by the current sources 102-1, 102-2, . . . , 102-N. In someembodiments, the current to voltage converter is configured to generatea voltage that is proportional to the currents, I₁, I₂, . . . , I_(N),or a sum of the currents, I₁, I₂, . . . , I_(N).

FIG. 3 depicts a current to voltage converter 306, which is anembodiment of the current to voltage converter 106 depicted in FIG. 1.However, the current to voltage converter 106 depicted in FIG. 1 is notlimited to the embodiment shown in FIG. 3. In the embodiment depicted inFIG. 3, the current to voltage converter 306 includes a resistor 336 andan amplifier 338. In some embodiments, the amplifier is an operationalamplifier (op-amp). In the embodiment depicted in FIG. 3, the resistorhas a fixed resistance value, “R.” However, in other embodiments, theresistor may have a variable resistance value. In an example of theoperation of the current to voltage converter 206, the amplifier and theresistor receive the currents, I₁, I₂, . . . , I_(N) that are generatedby the current sources 102-1, 102-2, . . . , 102-N of the activeshielding device 100 depicted in FIG. 1 and generates an output voltage,“V_(OUT),” which may be proportional to the sum of the currents, I₁, I₂,. . . , I_(N). In an embodiment, the output voltage, V_(OUT), can beexpressed as:

V _(OUT) =R×(I ₁ +I ₂ + . . . +I _(N)).  (1)

Although the illustrated current to voltage converter is shown withcertain components and described with certain functionality herein,other embodiments of the current to voltage converter may include feweror more components to implement the same, less, or more functionality.For example, the current to voltage converter may include more than oneamplifier and/or resistor or use different schemes/designs.

Turning back to FIG. 1, the voltage comparator 108 of the activeshielding device 100 is configured to compare at least one voltage thatis generated by the current to voltage converter 106 with at least onereference voltage. In some embodiments, the voltage comparator isconfigured to compare a voltage that is generated by the current tovoltage converter 106 with multiple reference voltages. Based on thecomparison result between the voltage that is generated by the currentto voltage converter and the at least one reference voltage, it can bedetermined whether or not the electrical cables or wires within theanalog wire shield unit 104 are tampered with (e.g., voltage probingthat involves cutting into the electrical cables or wires within theanalog wire shield unit or altering at least one voltage or current inthe electrical cables or wires within the analog wire shield unit. Insome embodiments, if the voltage that is generated by the current tovoltage converter is identical with the at least one reference voltageor within a threshold (e.g., ±1%) to the at least one reference voltage,it is determined that the electrical cables or wires within the analogwire shield unit are not tampered with. In these embodiments, if thevoltage that is generated by the current to voltage converter isdifferent from the at least one reference voltage or not within athreshold (e.g., ±1%) to the at least one reference voltage, it isdetermined that the electrical cables or wires within the analog wireshield unit are tampered with. In some embodiments, the active shieldingdevice includes a controller that is configured to determine whether ornot the electrical cables or wires within the analog wire shield unitare tampered with. The controller may be implemented in hardware (e.g.,circuit or circuits), software, firmware, or a combination thereof. Inan embodiment, the controller is implemented using a processor, such asa microcontroller, a host processor, a host, a digital signal processor(DSP), or a central processing unit (CPU). In some embodiments, thecontroller is configured to shut down or disable the circuit to beprotected 110 if the electrical cables or wires within the analog wireshield unit are tampered with.

FIG. 4 depicts a voltage comparator 408, which is an embodiment of thevoltage comparator 108 depicted in FIG. 1. However, the voltagecomparator 108 depicted in FIG. 1 is not limited to the embodiment shownin FIG. 4. In the embodiment depicted in FIG. 4, the voltage comparator408 includes two voltage comparison circuits 446-1, 446-2. In an exampleof the operation of the voltage comparator, the voltage comparisoncircuit 446-1 compares the output voltage, V_(OUT), from the current tovoltage converter 306 with a reference voltage, Vref+Δ, while thevoltage comparison circuit 446-2 compares the output voltage, V_(OUT),from the current to voltage converter with a reference voltage, Vref−Δ.A result signal is generated based on the comparison results of thevoltage comparison circuits 446-1, 446-2. Although the illustratedvoltage comparator is shown with certain components and described withcertain functionality herein, other embodiments of the voltagecomparator may include fewer or more components to implement the same,less, or more functionality. For example, the voltage comparator mayinclude a single voltage comparison circuit or more than two voltagecomparison circuit for different degree of voltage comparison precision.

In some embodiments, one or more switches are used to select one or moreof the current sources 102-1, 102-2, . . . , 102-N to apply to theanalog wire shield unit 104. Consequently, voltages on the analog wireshield unit may vary, depending upon how many current source(s) or whichof the current sources is/are selected, which makes it more difficultfor an attacker to access information by probing a voltage of the analogwire shield unit. FIG. 5 depicts an active shielding device 500 thatincludes multiple switches 550-1, 550-2, . . . , 550-N to controlmultiple current sources 502-1, 502-2, . . . , 502-N in accordance withan embodiment of the invention. In the embodiment depicted in FIG. 5,the active shielding device includes the current sources 502-1, 502-2, .. . , 502-N, an analog wire shield unit 504 connected to the currentsources, a current to voltage converter 506 connected to the analog wireshield unit, a voltage comparator 508 connected to the current tovoltage converter, the switches 550-1, 550-2, . . . , 550-N, and anoptional controller 552. The current sources 502-1, 502-2, . . . ,502-N, the analog wire shield unit 504, the current to voltage converter506, and the voltage comparator 508 in the embodiment depicted in FIG. 5are the same as or similar to the current sources 102-1, 102-2, . . . ,102-N, the analog wire shield unit 104, the current to voltage converter106, and the voltage comparator 108 in the embodiment depicted in FIG.1, respectively. Although the illustrated active shielding device 500 isshown with certain components and described with certain functionalityherein, other embodiments of the active shielding device may includefewer or more components to implement the same, less, or morefunctionality. For example, the active shielding device may include morethan one analog wire shield unit. In another example, in someembodiments, the active shielding device may include more than onecurrent to voltage converter and more than one voltage comparator. Theactive shielding device can operate in a first operational mode in whichthe active shielding device uses random data or known sequence to drivevalues on electrical cables or wires between the current sources and thecurrent to voltage converter and subsequently check the results from thevoltage comparator. The active shielding device can also operate in asecond operational mode that allows for a specific value to be writtento the active shielding device and a result be read back, which allowsthe active shielding device to be used as part of a secret that failswhen the active shielding device is broken.

In the embodiment depicted in FIG. 5, the current sources 502-1, 502-2,. . . , 502-N are configured to generate multiple currents, I₁, I₂, . .. , I_(N). The current sources can be implemented using various types ofcurrent sources that are known in the art. In some embodiments, thecurrents generated by the current sources are different from each other(i.e., each current source generates a unique current). In otherembodiments, at least two of the currents, I₁, I₂, . . . , I_(N),generated by the current sources are identical to each other. In theembodiment depicted in FIG. 5, the current sources are connected inparallel to each other such that each of the currents, I₁, I₂, . . . ,I_(N), flows through the analog wire shield unit 504 in parallel.

In the embodiment depicted in FIG. 5, the analog wire shield unit 504 isconnected between the current sources 502-1, 502-2, . . . , 502-N andthe current to voltage converter 506. The analog wire shield unit mayinclude one or more electrical cables or wires, which are made ofconductive materials (e.g., metals). In some embodiments, the analogwire shield unit includes multiple analog wire windings that areconnected between the current sources and the current to voltageconverter. In these embodiments, each of the current sources isconnected to a different analog wire winding of the analog wirewindings.

In the embodiment depicted in FIG. 5, the current to voltage converter506 is configured to generate at least one voltage in response to thecurrents, I₁, I₂, . . . , I_(N), that are generated by the currentsources 502-1, 502-2, . . . , 502-N. In some embodiments, the current tovoltage converter is configured to generate a voltage that isproportional to the currents, I₁, I₂, . . . , I_(N), or a sum of thecurrents, I₁, I₂, . . . , I_(N).

In the embodiment depicted in FIG. 5, the voltage comparator 508 isconfigured to compare at least one voltage that is generated by thecurrent to voltage converter 506 with at least one reference voltage. Insome embodiments, the voltage comparator is configured to compare avoltage that is generated by the current to voltage converter 506 withmultiple reference voltages. Based on the comparison result between thevoltage that is generated by the current to voltage converter and the atleast one reference voltage, it can be determined whether or not theelectrical cables or wires within the analog wire shield unit 504 aretampered with (e.g., voltage probing that involves cutting into theelectrical cables or wires within the analog wire shield unit oraltering at least one voltage or current in the electrical cables orwires within the analog wire shield unit. In some embodiments, if thevoltage that is generated by the current to voltage converter isidentical with the at least one reference voltage or within a threshold(e.g., ±1%) to the at least one reference voltage, it is determined thatthe electrical cables or wires within the analog wire shield unit arenot tampered with. In these embodiments, if the voltage that isgenerated by the current to voltage converter is different from the atleast one reference voltage or not within a threshold (e.g., ±1%) to theat least one reference voltage, it is determined that the electricalcables or wires within the analog wire shield unit are tampered with.

In the embodiment depicted in FIG. 5, the switches 550-1, 550-2, . . . ,550-N are connected between the current sources 502-1, 502-2, . . . ,502-N and the analog wire shield unit 504 and are configured to selectone or more of the current sources to apply to the analog wire shieldunit, based on control signals, D₁, D₂, . . . , D_(N). In the embodimentdepicted in FIG. 5, the controller 552 is configured to generate controlsignals, D₁, D₂, . . . , D_(N) to control the switches 550-1, 550-2, . .. , 550-N and/or the current to voltage converter 506. By controllingthe switches and/or the current to voltage converter, voltages on theanalog wire shield unit can vary (e.g., depending upon how many currentsource(s) or which of the current sources is/are selected), which makesit difficult for an attacker to access information by probing a voltageof the analog wire shield unit. The controller may be implemented inhardware (e.g., circuit or circuits), software, firmware, or acombination thereof. In an embodiment, the controller is implementedusing a processor, such as a microcontroller, a host processor, a host,a DSP, or a CPU. The control signals, D₁, D₂, . . . , D_(N) may bedigital signals, which can be random digital signals/sequences orpre-defined digital signals/sequences. In some embodiments, thecontroller includes a random number generator configured to generaterandom digital sequences. Although the controller is shown in FIG. 5 asbeing a component of the active shielding device 500, in otherembodiments, the controller is external to the active shielding device.In some embodiments, the controller is configured to determine whetheror not the electrical cables or wires within the analog wire shield unitare tampered with. In some embodiments, the controller is configured toshut down or disable a circuit to be protected, which can be connectedto electrical wires or cables within the analog wire shield unit,electrical wires or cables between the current sources and the analogwire shield unit, or electrical wires or cables between the analog wireshield unit and the current to voltage converter, if the electricalcables or wires within the analog wire shield unit are tampered with. Insome embodiments, digital active shielding can be combined with analogactive shielding to provide more complex protection against invasiveattacks. In some embodiments, one or more digital logic circuits areserially connected with an electrical cable or wire such that signals inthe electrical cable or wire can be altered by the digital logiccircuits. For example, voltages on the electrical cable or wire mayvary, depending upon the place or section at which the electrical cableor wire is probed, which makes it more difficult for an attacker toaccess information by probing the voltage at the electrical cable orwire.

In some embodiments, multiple sets of current sources, current tovoltage converters, and voltage comparators are used with an analog wireshield unit. Consequently, voltages on the analog wire shield unit maybe verified or validated repetitively, which makes it more difficult foran attacker to access information by probing a voltage of the analogwire shield unit. FIG. 6 depicts an active shielding device 600 thatincludes multiple sets of current sources 602-1, 602-2, . . . , 602-N,612-1, 612-2, . . . , 612-N, 622-1, 622-2, . . . , 622-N, 632-1, 632-2,. . . , 632-N, current to voltage converters 606-1, 606-2, and voltagecomparators 608-1, 608-2, 608-3 in accordance with an embodiment of theinvention. In the embodiment depicted in FIG. 6, the active shieldingdevice includes a first set of current sources 602-1, 602-2, . . . ,602-N, a second set of current sources 612-1, 612-2, . . . , 612-N, athird set of current sources 622-1, 622-2, . . . , 622-N, and a fourthset of current sources 632-1, 632-2, . . . , 632-N, an analog wireshield unit 604 connected to the current sources, first and secondcurrent to voltage converters 606-1, 606-2 connected to the analog wireshield unit, first and second voltage comparators 608-1, 608-2 connectedto the current to voltage converters, and a third voltage comparator608-3 connected to the first and second voltage comparators 608-1,608-2. The current sources 602-1, 602-2, . . . , 602-N, 612-1, 612-2, .. . , 612-N, 622-1, 622-2, . . . , 622-N, 632-1, 632-2, . . . , 632-N,the analog wire shield unit 604, the current to voltage converters606-1, 606-2, and the voltage comparators 608-1, 608-2, 608-3 in theembodiment depicted in FIG. 6 are the same as or similar to the currentsources 102-1, 102-2, . . . , 102-N, the analog wire shield unit 104,the current to voltage converter 106, and the voltage comparator 108 inthe embodiment depicted in FIG. 1, respectively. Although theillustrated active shielding device 600 is shown with certain componentsand described with certain functionality herein, other embodiments ofthe active shielding device may include fewer or more components toimplement the same, less, or more functionality. For example, the activeshielding device may include more than one analog wire shield unit.

In the embodiment depicted in FIG. 6, each of the first set of currentsources 602-1, 602-2, . . . , 602-N, the second set of current sources612-1, 612-2, . . . , 612-N, the third set of current sources 622-1,622-2, . . . , 622-N, and the fourth set of current sources 632-1,632-2, . . . , 632-N is configured to generate multiple currents, I₁,I₂, . . . , I_(N). The current sources can be implemented using varioustypes of current sources that are known in the art. In some embodiments,the currents generated by the current sources are different from eachother (i.e., each current source generates a unique current). In otherembodiments, at least two of the currents, I₁, I₂, . . . , I_(N),generated by the current sources are identical to each other. In theembodiment depicted in FIG. 6, each current source within one of thefirst, second, third, and fourth sets of current sources is connected inparallel to each other such that each of the currents, I₁, 1 ₂, . . . ,I_(N), flows through the analog wire shield unit 604 in parallel.

In the embodiment depicted in FIG. 6, the analog wire shield unit 604 isconnected to the second set of current sources 612-1, 612-2, . . . ,612-N, and to the fourth set of current sources 632-1, 632-2, . . . ,632-N. The analog wire shield unit may include one or more electricalcables or wires, which are made of conductive materials (e.g., metals).In some embodiments, the analog wire shield unit includes multipleanalog wire windings that are connected between the second set ofcurrent sources 612-1, 612-2, . . . , 612-N or the fourth set of currentsources 632-1, 632-2, . . . , 632-N and the current to voltageconverters 606-1, 606-2. In these embodiments, each current sourcewithin the second set of current sources 612-1, 612-2, . . . , 612-N isconnected to a different analog wire winding of the analog wirewindings, and/or each current source within the fourth set of currentsources 632-1, 632-2, . . . , 632-N is connected to a different analogwire winding of the analog wire windings.

In the embodiment depicted in FIG. 6, the first current to voltageconverter 606-1 is connected to the first set of current sources 602-1,602-2, . . . , 602-N and to the fourth set of current sources 632-1,632-2, . . . , 632-N through the analog wire shield unit 604. The firstcurrent to voltage converter 604-1 is configured to generate a firstoutput voltage, V_(out1), in response to the currents, I₂, . . . ,I_(N), that are generated by the first and fourth sets of currentsources 602-1, 602-2, . . . , 602-N, 632-1, 632-2, . . . , 632-N. Insome embodiments, the first output voltage, V_(out1), is proportional tothe currents, I₁, I₂, . . . , I_(N), or a sum of the currents, I₁, I₂, .. . , I_(N).

In the embodiment depicted in FIG. 6, the first voltage comparator 608-1is connected to the first current to voltage converter 606-1 andconfigured to compare the first output voltage, V_(out1), with at leastone reference voltage to generate a result signal, CMP1, which may be ananalog signal or a digital signal. In some embodiments, the firstvoltage comparator includes multiple voltage comparison circuitsconfigured to compare the first output voltage, V_(out1), with multiplereference voltages.

In the embodiment depicted in FIG. 6, the second current to voltageconverter 606-2 is connected to the second set of current sources 612-1,612-2, . . . , 612-N and to the third set of current sources 622-1,622-2, . . . , 622-N through the analog wire shield unit 604. The secondcurrent to voltage converter is configured to generate a second outputvoltage, V_(out2), in response to the currents, I₁, I₂, . . . , I_(N),that are generated by the second and third sets of current sources612-1, 612-2, . . . , 612-N, 622-1, 622-2, . . . , 622-N. In someembodiments, the second output voltage, V_(out2), is proportional to thecurrents, I₁, I₂, . . . , I_(N), or a sum of the currents, I₁, I₂, . . ., I_(N).

In the embodiment depicted in FIG. 6, the second voltage comparator608-2 is connected to the second current to voltage converter 606-2 andconfigured to compare the second output voltage, V_(out2), with at leastone reference voltage to generate a result signal, CMP2, which may be ananalog signal or a digital signal. In some embodiments, the firstvoltage comparator includes multiple voltage comparison circuitsconfigured to compare the second output voltage, V_(out1), with multiplereference voltages.

In the embodiment depicted in FIG. 6, the third voltage comparator 608-3is configured to compare the result signal, CMP1, from the first voltagecomparator 608-1 and the result signal, CMP2, from the second voltagecomparator 608-2 to generate a comparison result. Based on thecomparison result from the third voltage comparator, it can bedetermined whether or not the electrical cables or wires within theanalog wire shield unit 604 are tampered with (e.g., voltage probingthat involves cutting into the electrical cables or wires within theanalog wire shield unit or altering at least one voltage or current inthe electrical cables or wires within the analog wire shield unit. Insome embodiments, if the result signal, CMP1, from the first voltagecomparator 608-1 is identical with the result signal, CMP2, from thesecond voltage comparator 608-2 or within a threshold (e.g., ±1%) to theresult signal, CMP2, from the second voltage comparator 608-2, it isdetermined that the electrical cables or wires within the analog wireshield unit are not tampered with. In these embodiments, if the resultsignal, CMP1, from the first voltage comparator 608-1 is different fromthe result signal, CMP2, from the second voltage comparator 608-2 or notwithin a threshold (e.g., ±1%) to the result signal, CMP2, from thesecond voltage comparator 608-2, it is determined that the electricalcables or wires within the analog wire shield unit are tampered with. Insome embodiments, the active shielding device includes a controller thatis configured to determine whether or not the electrical cables or wireswithin the analog wire shield unit are tampered with. The controller maybe implemented in hardware (e.g., circuit or circuits), software,firmware, or a combination thereof. In an embodiment, the controller isimplemented using a processor, such as a microcontroller, a hostprocessor, a host, a DSP, or a CPU. In some embodiments, the controlleris configured to shut down or disable a circuit to be protected, whichcan be connected to electrical wires or cables within the analog wireshield unit, electrical wires or cables between the current sources andthe analog wire shield unit, or electrical wires or cables between theanalog wire shield unit and the current to voltage converters, if theelectrical cables or wires within the analog wire shield unit aretampered with. In some embodiments, digital active shielding can becombined with analog active shielding to provide more complex protectionagainst invasive attacks. In some embodiments, one or more digital logiccircuits are serially connected with an electrical cable or wire suchthat signals in the electrical cable or wire can be altered by thedigital logic circuits. For example, voltages on the electrical cable orwire may vary, depending upon the place or section at which theelectrical cable or wire is probed, which makes it more difficult for anattacker to access information by probing the voltage at the electricalcable or wire.

In some embodiments, one or more switches are used to select one or moreof the current sources 602-1, 602-2, . . . , 602-N, 612-1, 612-2, . . ., 612-N, 622-1, 622-2, . . . , 622-N, 632-1, 632-2, . . . , 632-N toapply to the analog wire shield unit 604, the first current to voltageconverter 606-1, or the second current to voltage converter 606-2.Consequently, voltages on the analog wire shield unit may vary,depending upon how many current source(s) or which of the currentsources is/are selected, which makes it more difficult for an attackerto access information by probing a voltage of the analog wire shieldunit. FIG. 7 depicts an active shielding device 700 that includesmultiple switches 750-1, 750-2, . . . , 750-N, 760-1, 760-2, . . . ,760-N, 770-1, 770-2, . . . , 770-N, 780-1, 780-2, . . . , 780-N tocontrol the current sources 602-1, 602-2, . . . , 602-N, 612-1, 612-2, .. . , 612-N, 622-1, 622-2, . . . , 622-N, 632-1, 632-2, . . . , 632-N inaccordance with an embodiment of the invention. In the embodimentdepicted in FIG. 7, the active shielding device includes the currentsources 602-1, 602-2, . . . , 602-N, 612-1, 612-2, . . . , 612-N, 622-1,622-2, . . . , 622-N, 632-1, 632-2, . . . , 632-N, the analog wireshield unit 604 connected to the current sources, the first and secondcurrent to voltage converters 606-1, 606-2 connected to the analog wireshield unit, the first and second voltage comparators 608-1, 608-2connected to the current to voltage converters, the third voltagecomparator 608-3 connected to the first and second voltage comparators608-1, 608-2, the switches 750-1, 750-2, . . . , 750-N, 760-1, 760-2, .. . , 760-N, 770-1, 770-2, . . . , 770-N, 780-1, 780-2, . . . , 780-N,and an optional controller 752. The switches 750-1, 750-2, . . . ,750-N, 760-1, 760-2, . . . , 760-N, 770-1, 770-2, . . . , 770-N, 780-1,780-2, . . . , 780-N and the controller 752 in the embodiment depictedin FIG. 7 are the same as or similar to the switches 550-1, 550-2, . . ., 550-N and the controller 552 in the embodiment depicted in FIG. 5,respectively. Although the illustrated active shielding device 700 isshown with certain components and described with certain functionalityherein, other embodiments of the active shielding device may includefewer or more components to implement the same, less, or morefunctionality. For example, the active shielding device may include morethan one analog wire shield unit.

In the embodiment depicted in FIG. 7, the switches 750-1, 750-2, . . . ,750-N, 760-1, 760-2, . . . , 760-N, 770-1, 770-2, . . . , 770-N, 780-1,780-2, . . . , 780-N are configured to select one or more of the currentsources 602-1, 602-2, . . . , 602-N, 612-1, 612-2, . . . , 612-N, 622-1,622-2, . . . , 622-N, 632-1, 632-2, . . . , 632-N to apply to the analogwire shield unit 604, the first current to voltage converter 606-1, orthe second current to voltage converter 606-2, based on control signals,D₁, D₂, . . . , D_(N). In the embodiment depicted in FIG. 7, thecontroller 752 is configured to generate control signals, D₁, D₂, . . ., D_(N) to control the switches 750-1, 750-2, . . . , 750-N, 760-1,760-2, . . . , 760-N, 770-1, 770-2, . . . , 770-N, 780-1, 780-2, . . . ,780-N and/or at least one of the first and second current to voltageconverters 606-1, 606-2. By controlling the switches and/or the currentto voltage converters, voltages on the analog wire shield unit can vary(e.g., depending upon how many current source(s) or which of the currentsources is/are selected), which makes it difficult for an attacker toaccess information by probing a voltage of the analog wire shield unit.The controller may be implemented in hardware (e.g., circuit orcircuits), software, firmware, or a combination thereof. In anembodiment, the controller is implemented using a processor, such as amicrocontroller, a host processor, a host, a DSP, or a CPU. The controlsignals, D₁, D₂, . . . , D_(N) may be digital signals, which can berandom digital signals/sequences or pre-defined digitalsignals/sequences. In some embodiments, the controller includes a randomnumber generator configured to generate random digital sequences.Although the controller is shown in FIG. 7 as being a component of theactive shielding device 700, in other embodiments, the controller isexternal to the active shielding device. In some embodiments, thecontroller is configured to shut down or disable a circuit to beprotected, which can be connected to electrical wires or cables withinthe analog wire shield unit, electrical wires or cables between thecurrent sources and the analog wire shield unit, or electrical wires orcables between the analog wire shield unit and the current to voltageconverters 606-1, 606-2, if the electrical cables or wires within theanalog wire shield unit are tampered with.

Digital active shielding can be combined with analog active shielding toprovide more complex protection against invasive attacks. In someembodiments, one or more digital logic circuits are serially connectedwith an electrical cable or wire such that signals in the electricalcable or wire can be altered by the digital logic circuits. For example,even number (e.g., 2, 4, 6, 8, 14, 20) of inverters can be seriallyconnected with an electrical cable or wire such that when a digitalsignal flows through these inverters, the output signal of the evennumber of inverters is identical with the original signal. However, whenan attacker probes the electrical cable or wire, the probed voltage maynot correspond to the original digital signal. For example, when anattacker probes the electrical cable or wire after an odd number ofinverters, the probed voltage corresponds to an inverted version of theoriginal digital signal. However, when an attacker probes the electricalcable or wire after an even number of inverters, the probed voltagecorresponds to the original digital signal. Consequently, voltages onthe electrical cable or wire may vary, depending upon the place orsection at which the electrical cable or wire is probed, which makes itmore difficult for an attacker to access information by probing thevoltage at the electrical cable or wire.

FIG. 8 depicts an active shielding device 800 that includes acombination of a digital shielding unit 854 and the analog wire shieldunit 604 in accordance with an embodiment of the invention. In theembodiment depicted in FIG. 8, the active shielding device includes thecurrent sources 602-1, 602-2, . . . , 602-N, 612-1, 612-2, . . . ,612-N, 622-1, 622-2, . . . , 622-N, 632-1, 632-2, . . . , 632-N, theanalog wire shield unit 604 connected to the current sources, the firstand second current to voltage converters 606-1, 606-2 connected to theanalog wire shield unit, the first and second voltage comparators 608-1,608-2 connected to the current to voltage converters, the third voltagecomparator 608-3 connected to the first and second voltage comparators608-1, 608-2, the switches 750-1, 750-2, . . . , 750-N, 760-1, 760-2, .. . , 760-N, 770-1, 770-2, . . . , 770-N, 780-1, 780-2, . . . , 780-N,an optional controller 852, the digital shielding unit 854 connected tothe current sources, two digital logics 856-1, 856-2, and a digitalcomparator 858. The switches 750-1, 750-2, . . . , 750-N, 760-1, 760-2,. . . , 760-N, 770-1, 770-2, . . . , 770-N, 780-1, 780-2, . . . , 780-Nand the controller 852 in the embodiment depicted in FIG. 8 are the sameas or similar to the switches 550-1, 550-2, . . . , 550-N and thecontroller 552 in the embodiment depicted in FIG. 5, respectively.Although the illustrated active shielding device 800 is shown withcertain components and described with certain functionality herein,other embodiments of the active shielding device may include fewer ormore components to implement the same, less, or more functionality. Forexample, the active shielding device may include more than one digitalshielding unit and/or more than one analog wire shield unit.

In the embodiment depicted in FIG. 8, the digital shielding unit 854 isconnected between the second set of current sources 612-1, 612-2, . . ., 612-N, and to the third set of current sources 622-1, 622-2, . . . ,622-N. In the embodiment depicted in FIG. 8, the digital shielding unitincludes a first set of inverters 866-1, 866-2, . . . , 866-K, where Kis a positive even integer, which is connected between the second set ofcurrent sources 612-1, 612-2, . . . , 612-N, and to the third set ofcurrent sources 622-1, 622-2, . . . , 622, and a second set of inverters876-1, 876-2, . . . , 876-K, which is connected between the digitallogic 856-2 and the digital comparator 858. The digital shielding unitmay include one or more electrical cables or wires, which are made ofconductive materials (e.g., metals). In some embodiments, the electricalcables or wires within the digital shielding unit is located to the topmetal layer of the digital shielding unit 854. When an attacker probesthe electrical cables or wires, the probed voltage may not correspond tothe original digital signal. For example, when an attacker probes theelectrical cable or wire after an odd number of inverters, the probedvoltage corresponds to an inverted version of the original digitalsignal. However, when an attacker probes the electrical cable or wireafter an even number of inverters, the probed voltage corresponds to theoriginal digital signal. Consequently, voltages on the electrical cableor wire may vary, depending upon the place or section at which theelectrical cable or wire is probed, which makes it more difficult for anattacker to access information by probing the voltage at the electricalcable or wire. Although the illustrated the digital shielding unit 854is shown with certain components and described with certainfunctionality herein, other embodiments of the digital shielding unitmay include fewer or more components to implement the same, less, ormore functionality. For example, the digital shielding unit may includeonly one set of even number of inverters.

In the embodiment depicted in FIG. 8, the controller 852 is configuredto generate digital control signals, D₁, D₂, . . . , D_(M), where M is apositive integer that is greater than one, which may be random digitalsignals/sequences or pre-defined digital signals/sequences. Thecontroller may be implemented in hardware (e.g., circuit or circuits),software, firmware, or a combination thereof. In an embodiment, thecontroller is implemented using a processor, such as a microcontroller,a host processor, a host, a DSP, or a CPU. In some embodiments, thecontroller includes a random number generator configured to generaterandom digital sequences. The control signals, D₁, D₂, . . . , D_(N),where N is an integer that is smaller than M, to control the switches750-1, 750-2, . . . , 750-N, 760-1, 760-2, . . . , 760-N, 770-1, 770-2,. . . , 770-N, 780-1, 780-2, . . . , 780-N. By controlling the switches,voltages on the analog wire shield unit 604 can vary (e.g., dependingupon how many current source(s) or which of the current sources is/areselected), which makes it difficult for an attacker to accessinformation by probing a voltage of the analog wire shield unit.Although the controller is shown in FIG. 8 as being a component of theactive shielding device 800, in other embodiments, the controller isexternal to the active shielding device. In some embodiments, thecontroller is configured to shut down or disable a circuit to beprotected, which can be connected to electrical wires or cables withinthe analog wire shield unit, electrical wires or cables between thecurrent sources and the analog wire shield unit, or electrical wires orcables between the current to voltage converters 606-1, 606-2 and theanalog wire shield unit, if the electrical cables or wires within theanalog wire shield unit are tampered with.

In the embodiment depicted in FIG. 8, the digital logic 856-1 isconfigured to generate a result signal, OUTi, based on the digitalsignals, D₁, D₂, . . . , D_(M). The digital logic 856-2 is configured togenerate a result signal, OUTo, based on the digital signals, D₁, D₂, .. . , D_(M). The digital logics 856-1, 856-2 are identical digitalcircuits and/or configured to perform identical functions. In someembodiments, the digital logics are digital gates such as NAND gates, ORgates or XOR gates, or more complex digital logics. The digitalcomparator 858 is configured to compare the result signal, OUTi, fromthe digital logic 856-1 with the result, OUTo, from the digital logic856-2 to generate a digital comparison result. Based on the digitalcomparison result from the digital comparator, it can be determinedwhether or not the electrical cables or wires within the digitalshielding unit 854 are tampered with (e.g., voltage probing thatinvolves cutting into the electrical cables or wires within the digitalshielding unit or altering at least one voltage or current in theelectrical cables or wires within the digital shielding unit. In someembodiments, if the result signal, OUTi, from the digital logic 856-1 isidentical with the result, OUTo, from the digital logic 856-2, it isdetermined that the electrical cables or wires within the digitalshielding unit are not tampered with. In these embodiments, if theresult signal, OUTi, from the digital logic 856-1 is different from theresult, OUTo, from the digital logic 856-2, it is determined that theelectrical cables or wires within the digital shielding unit aretampered with. In some embodiments, the active shielding device includesa controller (e.g., the controller 852) that is configured to determinewhether or not the electrical cables or wires within the digitalshielding unit are tampered with. The controller may be implemented inhardware (e.g., circuit or circuits), software, firmware, or acombination thereof. In an embodiment, the controller is implementedusing a processor, such as a microcontroller, a host processor, a host,a DSP, or a CPU. In some embodiments, the controller is configured toshut down or disable a circuit to be protected, which can be connectedto electrical wires or cables within the digital shielding unit,electrical wires or cables between the current sources and the digitalshielding unit, or electrical wires or cables between the digitalshielding unit and the digital comparator, if the electrical cables orwires within the digital shielding unit are tampered with.

FIG. 9 is a process flow diagram of a method for active shielding inaccordance to an embodiment of the invention. According to the method,at block 902, currents are generated using an active shielding device.At block 904, the currents are conducted through analog wire windings ofthe active shielding device. At block 906, a voltage is generated inresponse to the currents using a current to voltage converter of theactive shielding device. At block 908, the voltage is compared with areference voltage using a voltage comparator of the active shieldingdevice. The active shielding device may be similar to, the same as, or acomponent of the active shielding device 100 depicted in FIG. 1, theactive shielding device 500 depicted in FIG. 5, the active shieldingdevice 600 depicted in FIG. 6, and/or the active shielding device 700depicted in FIG. 7.

FIG. 10 is a process flow diagram of a method for active shielding inaccordance to another embodiment of the invention. According to themethod, at block 1002, currents are generated using an active shieldingdevice. At block 1004, the currents are conducted through analog wirewindings of the active shielding device in response to a digital controlsequence. At block 1006, a voltage is generated in response to thecurrents using a current to voltage converter of the active shieldingdevice. At block 1008, the voltage is compared with a reference voltageusing a voltage comparator of the active shielding device. At block1010, the digital control sequence is processed before conducting thedigital control sequence through inverters of an active shielding unitof the active shielding device and after conducting the digital controlsequence through the inverters using digital logics of the activeshielding device to generate a first processing result signal and asecond result signal, respectively. At black 1012, the first processingresult signal is compared with the second result signal. The activeshielding device may be similar to, the same as, or a component of theactive shielding device 800 depicted in FIG. 8.

Although the operations of the method(s) herein are shown and describedin a particular order, the order of the operations of each method may bealtered so that certain operations may be performed in an inverse orderor so that certain operations may be performed, at least in part,concurrently with other operations. In another embodiment, instructionsor sub-operations of distinct operations may be implemented in anintermittent and/or alternating manner.

It should also be noted that at least some of the operations for themethods described herein may be implemented using software instructionsstored on a computer useable storage medium for execution by a computer.As an example, an embodiment of a computer program product includes acomputer useable storage medium to store a computer readable program.

The computer-useable or computer-readable storage medium can be anelectronic, magnetic, optical, electromagnetic, infrared, orsemiconductor system (or apparatus or device). Examples ofnon-transitory computer-useable and computer-readable storage mediainclude a semiconductor or solid-state memory, magnetic tape, aremovable computer diskette, a random-access memory (RAM), a read-onlymemory (ROM), a rigid magnetic disk, and an optical disk. Currentexamples of optical disks include a compact disk with read only memory(CD-ROM), a compact disk with read/write (CD-R/W), and a digital videodisk (DVD).

Alternatively, embodiments of the invention may be implemented entirelyin hardware or in an implementation containing both hardware andsoftware elements. In embodiments which use software, the software mayinclude but is not limited to firmware, resident software, microcode,etc.

Although specific embodiments of the invention have been described andillustrated, the invention is not to be limited to the specific forms orarrangements of parts so described and illustrated. The scope of theinvention is to be defined by the claims appended hereto and theirequivalents.

What is claimed is:
 1. An active shielding device, the active shield device comprising: a plurality of current sources configured to generate a plurality of currents; an analog wire shield unit connected to the current sources; a plurality of switches connected between the current sources and the analog wire shield unit; a current to voltage converter connected to the analog wire shield unit and configured to generate a voltage in response to the currents that are generated by the current sources and a digital control sequence for the switches; a voltage comparator connected to the current to voltage converter and configured to compare the voltage that is generated by the current to voltage converters with a reference voltage; a digital active shielding unit connected to the current sources; a plurality of digital logics configured to process the digital control sequence before conducting the digital control sequence through the digital active shielding unit and after conducting the digital control sequence through the digital active shielding unit to generate a first processing result signal and a second result signal; and a digital comparator configured to compare the first processing result signal with the second result signal.
 2. The active shielding device of claim 1, wherein the digital active shielding unit comprises an even number of inverters.
 3. The active shielding device of claim 1, wherein the digital logics are identical to each other.
 4. The active shielding device of claim 1, wherein one of the digital logics is connected to the switches through the digital active shielding unit.
 5. The active shielding device of claim 1, wherein the current sources are connected in parallel to each other.
 6. The active shielding device of claim 1, wherein the analog wire shield unit comprises a plurality of analog wire windings that are connected between the current sources and the current to voltage converter.
 7. The active shielding device of claim 6, wherein each of the analog wire windings is connected to a different current source of the current source.
 8. The active shielding device of claim 1, further comprising: a controller configured to generate the digital control sequence
 9. The active shielding device of claim 8, wherein the controller comprises a random number generator.
 10. An active shielding device, the active shield device comprising: first, second, third, and fourth sets of current sources, wherein each of the first, second, third, and fourth sets of current sources is configured to generate a plurality of currents; an analog wire shield unit connected to the second and fourth sets of current sources; first, second, third, and fourth sets of switches that are connected to the first, second, third, and fourth sets of current sources, respectively, and are controlled by a digital control sequence; a first current to voltage converter connected to the first set of current sources and to the fourth set of current sources through the analog wire shield unit, wherein the first current to voltage converter is configured to generate a first voltage in response to the currents that are generated by the first and fourth sets of current sources; a first voltage comparator connected to the first current to voltage converter and configured to compare the first voltage with a first reference voltage; a second current to voltage converter connected to the second set of current sources and to the third set of current sources through the analog wire shield unit, wherein the second current to voltage converter is configured to generate a second voltage in response to the currents that are generated by the second and third sets of current sources; a second voltage comparator connected to the second current to voltage converter and configured to compare the second voltage with a second reference voltage; a third voltage comparator configured to compare results from the first voltage comparator and from the second voltage comparator; a digital active shielding unit connected to the second and third sets of current sources; a plurality of digital logics configured to process the digital control sequence before conducting the digital control sequence through the digital active shielding unit and after conducting the digital control sequence through the digital active shielding unit to generate a first processing result signal and a second result signal; and a digital comparator configured to compare the first processing result signal with the second result signal.
 11. The active shielding device of claim 10, wherein the digital active shielding unit comprises an even number of inverters.
 12. The active shielding device of claim 10, wherein the digital logics are identical to each other.
 13. The active shielding device of claim 10, wherein one of the digital logics is connected to the switches through the digital active shielding unit.
 14. The active shielding device of claim 10, wherein each current source within one of the first, second, third, and fourth sets of current sources is connected in parallel to each other.
 15. The active shielding device of claim 10, wherein the analog wire shield unit comprises a plurality of analog wire windings that are connected between the fourth set of current sources and the first current to voltage converter and between the second set of current sources and the second current to voltage converter.
 16. The active shielding device of claim 10, wherein the first set of switches are connected between the first set of current sources and the first current to voltage converter, wherein the second set of switches are connected between the second set of current sources and the analog wire shield unit, wherein the third set of switches are connected between the third set of current sources and the second current to voltage converter, and wherein the fourth set of switches are connected between the fourth set of current sources and the analog wire shield unit.
 17. The active shielding device of claim 10, further comprising: a controller configured to generate the digital signal sequence to control the first, second, third, and fourth sets of switches.
 18. The active shielding device of claim 17, wherein the controller comprises a random number generator.
 19. A method for active shielding, the method comprising: generating a plurality of currents using an active shielding device; conducting the currents through a plurality of analog wire windings of an active shielding unit of the active shielding device in response to a digital control sequence; generating a voltage in response to the currents using a current to voltage converter of the active shielding device; comparing the voltage with a reference voltage using a voltage comparator of the active shielding device; processing the digital control sequence before conducting the digital control sequence through a plurality of inverters of an active shielding unit of the active shielding device and after conducting the digital control sequence through the inverters using a plurality of digital logics of the active shielding device to generate a first processing result signal and a second result signal, respectively; and comparing the first processing result signal with the second result signal.
 20. The method of claim 19, wherein the digital active shielding unit comprises an even number of inverters, and wherein the digital logics are identical to each other. 